Recovery of meta-2-xylidine



United States Patent Ol'ice RECOVERY OF META-Z-XYLIDINE Stanley F.Birch, Frederick A. Fidler, and Ronald A. Dean, Sunbury-ou-Thames,England, assignors to The British Petroleum Company Limited No Drawing.Original application May 21, 1947, Serial No. 749,598. Divided and thisapplication September 8, 1952, Serial No. 308,508

Claims priority, application Great Britain May 24, 1946 2 Claims. (Cl.260-582) The present invention relates to the recovery of meta-2-xy1idine from coal tar xylene.

Xylidines, which are used extensively in the manufacture of dye stufisand fine chemicals, are usually obtained by nitrating coal-tar xylene,and reducing the material so obtained to yield a mixture of the amines.These processes are well known in the art. The resulting amine mixtureis treated with acetic acid, and the acetate of meta-4-xylidine isseparated and the amine regenerated. The residue after separation of theacetate of meta-4- xylidine is treated with hydrochloric acid, and thehydrochloride of para-xylidine is separated and obtained in a pure stateby re-crystallisation from water.

In the following description the liquors remaining after there-crystallisation of para-xylidine hydrochloride from water arereferred to as mother liquors, and the residue remaining after theseparation of meta-4-xylidine and crude para-xylidine hydrochloride, ashereinbefore described, is referred to as xylidine residues. The knownprocess may be represented diagrammatically as follows:

Mixture of xylidines Treat withl acetic acid meta-'i-xylidine acetateResidue Treat with H01 recrystallisation from water pure para-xylidinehydrochloride Mother liquors (-15% on crude xylidine) It is the usualpresent day practice to treat the original mixture of xylidines for therecovery therefrom of meta- 4-xylidine and para-xylidine and to regardthe mother liquors and xylidine residues as waste products that are notfurther treated. Since the mother liquors amount to 10-15% of the crudexylidines and the xylidine residues amount to 25-35% of the crudexylidines, the present day practice is wasteful.

We have found that by a simple method it is possible to recoversubstantial yields of meta-Z-xylidine from the above referred to motherliquors:

According to the present invention the xylidine mother liquors from thecrystallisation of para-xylidine hydrochloride are treated with alkaliand the amines regenerated. The xylidines thus obtained are fractionatedin an etficient column having the equivalent of at least twenty actualplates operated at a reflux ratio of not less than :1 and under reducedpressure generally not exceeding 50 mm. mercury pressure, for theproduction of a light fraction boiling up to about 96 C. at 10.5 mm. of

2,717,269 Patented Sept. 6, 1955 mercury, which light fraction containsabout to of meta-Z-xylidine. The crude meta-2-xylidine thus obtained maybe further concentrated and purified according to known methods as bymeans of organic derivatives such as the forrnyl compound or through asalt formed with a mineral acid.

Preferably the xylidine mother liquors are admixed with aqueous sodiumhydroxide solution and steam distilled for the regeneration of the freeamines prior to fractional distillation in accordance with the processof the present invention.

The process of the present invention is illustrated but in no waylimited by the following example:

Example The amines recovered from the mother liquors remaining after therecrystallisation of p-xylidine hydrochloride as hereinfore describedwere distilled in a fractionating column equivalent to about 20theoretical plates, and the distillation was carried out at a pressureof 10.5 mm. of mercury. The fraction distilling between 94 and 96 wascollected and proved to be substantially meta-2- xylidine. This fractioncomprised 52% of the Whole. The discarded fractions from thisdistillation may be recycled for example for the crystallisation ofpara-xylidine hydrochloride, or to the hydrochloric acid treatment ofthe xylidines.

By the present process, a greater recovery of meta-2- xylidine isobtained by recovering the meta-2-xylidine from the p-xylidinerecrystallisation medium than from the original p-xylidine.crystallisation medium. This application is a divisional application ofapplication Serial Number 749,598, filed May 21, 1947, now Patent No.2,615,047.

We claim:

1. A process for the recovery of meta-Z-xylidine from xylidine motherliquors, said xylidine mother liquors having been obtained by treating acrude mixture of xylidines with acetic acid to form the acetateofmeta-4-xylidine and a residue, separating the acetate of meta-4-xylidinefrom the residue, treating the residue with hydrochloric acid to formcrude para-xylidine hydrochloride and Xylidine residues, separating saidpara-xylidine hydrochloride by recrystallisation from water obtainingpure para-xylidine hydrochloride and Xylidine mother liquors andseparating said mother liquors, which comprises regenerating free aminesfrom said mother liquors by treatment with alkali and fractionallydistilling said mother liquors in a fractionating column having theequivalent of at least 20 theoretical plates and operated at a refluxratio of not less than 15.1 and under a pressure not exceeding 50 mm.pressure of mercury to yield a fraction having a final boiling point notexceeding 96 C. at 10.5 mm. pressure of mercury and consistingessentially of meta-Z-xylidine.

2. A process as defined in claim 1 wherein the xylidine mother liquor isadmixed with an aqueous solution of sodium hydroxide and steam forregeneration of the free amine prior to the fractional distillation.

OTHER REFERENCES Hodgkinson, et al. Jour. Chem. Soc. (London), 1900,vol. 77, pp. 65-68.

1. A PROCESS FOR THE RECOVERY OF META-2-XYLIDINE FROM XYLIDINE MOTHERLIQUORS, SAID XYLIDINE MOTHER LIQUORS HAVING BEEN OBTAINED BY TREATING ACRUDE MIXTURE OF XYLIDINES WITH ACETIC ACID TO FORM THE ACETATE OFMETA-4-XYLIDINE AND A RESIDUE, SEPARATING THE ACETATE OF META-4-XYLIDINEFROM THE RESIDUE, TREATING THE RESIDUE WITH HYDROCHLORIC ACID TO FORMCRUDE PARA-XYLIDINE HYDROCHLORIDE AND XYLIDINE RESIDUES, SEPARATING SAIDPARA-XYLIDINE HYDROCHLORIDE BY RECRYSTALLISATION FROM WATER OBTAININGPURE PARA-XYLIDINE HYDROCHLORIDE AND XYLIDINE MOTHER LIQUORS ANDSEPARATING SAID MOTHER LIQUORS, WHICH COMPRISES REGENERATING FREE AMINESFROM SAID MOTHER LIQUORS BY TREATMENT WITH ALKALI AND FRACTIONALLYDISTILLING SAID MOTHER LIQUORS IN A FRACTIONATING COLUMN HAVING THEEQUIVALENT OF AT LEAST 20 THEORETICAL PLATES AND OPERATED AT A REFLUXRATIO OF NOT LESS THAN 15.1 AND UNDER A PRESSURE NOT EXCEEDING 50 MM.PRESSURE OF MERCURY TO YIELD A FRACTION HAVING A FINAL BOILING POINT NOTEXCEEDING 96* C. AT 10.5 MM. PRESSURE OF MERCURY AND CONSISTINGESSENTIALLY OF META-2-XYLIDINE.